The present invention relates to a communication method and equipment for freeze-frame video phone over standard telephone line, which transmit and receive freeze-frame video data in appropriate interval between the users.
In TTC standard (Nippon TTC JJ-40.10, "Communication Method for Freeze-Frame Video Phone over Standard Telephone Line," 1988. 5. 13), a dual tone signal of 1633 Hz and 2006 Hz is used as transient signal from voice communication mode to video data communication mode. Video data are carried by a modulated carrier wave, approximate frequency of 1747 Hz, after amplitude and phase modulation. In other words, approximately 1747 pixels are sent in a second. In the conventional communication method, however, first, the system can easily malfunction by dual tones of whistling voice of human, second, it is hard to classify more than 64 grey levels per pixel as the video data are transmitted in analog method, amplitude and phase modulation.